Investigators in Holland and the United States are trying to pinpoint the origin of needles found in turkey sandwiches served on Delta Air Lines flights between the two countries.

On Tuesday, a spokesperson for Amsterdam's Schiphol Airport Police said Dutch and U.S. detectives are co-ordinating their investigation. FBI Special Agent Stephen Emmett in Atlanta confirmed to The Associated Press that bureau is part of the probe, but provided no further details.

According to the airline, what appear to be 2.5-centimetre sewing needles were found in five sandwiches on Sunday.

Needles were found aboard two flights to Atlanta and one to Seattle. Two needles were also discovered in sandwiches aboard a Minneapolis-bound flight, one of which injured a passenger’s mouth.

"I figured it might be a toothpick," passenger Jim Tonjes of Plymouth, Minnesota, told the Star Tribune newspaper.

"It looked like a sewing needle but without an eye. ... I was in shock," he explained. "I thought, 'Oh, my God.' It's the last thing you expect in a sandwich."

All of the flights originated in at Schiphol Airport. The sandwiches were all made in the Amsterdam kitchen of Gate Gourmet, an airline catering company that handles meals for more than 3 million flights annually.

In a statement issued Monday, the company said it had launched its own investigation of what it considers a "criminal act" and was "heightening our already stringent safety and security procedures, to prevent any recurrence."

In its own written statement issued Monday, the airline said it is also taking the matter "extremely" seriously.

"Delta has taken immediate action with our in-flight caterer at Amsterdam to ensure the safety and quality of the food we provide onboard our aircraft," the airline said.

The U.S. Transportation Security Administration says it has notified other U.S. carriers with flights out of the Schiphol Airport.